The Phial of Galadriel was a crystal phial filled with water from her fountain which held the light of Eärendil's star - the light of the Two Trees as preserved in a Silmaril. Frodo used the mere touch of it to ease the thought of the One Ring when he, Sam Gamgee, and Gollum were watching the Witch-king lead his army out of Minas Morgul. He also used it while entering into Mordor to defend himself from the spider Shelob. When Shelob first approached, Sam reminded him of the "star-glass" and its light drove her away. Frodo gave the light to Sam to hold while he cut through Shelob's webbing and Sam wielded it when he attacked Shelob to rescue Frodo. The star-glass shone particularly bright in response to his indomitable spirit. He used it twice to get past the Two Watchers who guarded the tower of Cirith Ungol; the second time the phial shone out lightning-bright in tribute to his hardiness and faithfulness.
Sam also attempted to use the light in the Crack of Doom but the light was subdued by the power of the heart of Sauron's realm. The light was one of the items found on him when he and Frodo were rescued by the Eagles; Gandalf kept both it and Sam's box of Earth from Galadriel safe while the two hobbits were being healed after their collapse on the side of Mount Doom. The Phial of Galadriel seemed to inspire its bearers to call out to Elbereth, who is also known as Varda, as both Frodo and Sam call out in Elvish. Frodo also cries out "aiya Eärendil elenion ancalima!" the first time he uses it against Shelob. Although Frodo did not understand these words, they were in reference to Eärendil, and they translate as "hail Eärendil, brightest of stars!" from Quenya. At the end of the Third Age, the Light of Earendil went to the Uttermost West with Frodo.